Process for tanning animal hides with salts of iron



Patented June 10, 1930 UNITED STATES PATENT OFFICE KURT STIIBMER, OF IPBUHLITZ, GERMANY PROCESS FOR- TANNING' ANIMAL HIDES WITH SALTS'OF IRON 1T0 Drawing. Application filed February 12, 1929, Serial No. 339,497, and .in Germany February 18, 1928.

There is a known method of tanning animal hides by introducing divalent salts of iron (ferro salts) first into the fibre and by then om'dizing them into trivalent salts of 5 iron (ferri salts) Which are to be deposited on the fibre-through treatment with higher nitric oxides N' O NO also with nitric acid. A process has also become known in which -oxidation is carried out with a mixture of N0 and NO, whereby compound salts of iron (FeSO O) are formed.

All these processes have the disadvantage that the leather thereby obtained is brittle, as both N0 and N 0 like the nitric acid which is formed, immediately attack and finally destroy the fibre.

With this process, therefore, the gradual progress of oxidation cannot be regulated. Moreover, it is unavoidable that the top layers of the hide should be over-tanned, and the complete tanning through the hide is only obtained at the expense of the grained surface being prejudicially afiected. In addition to this, all the means of oxidation mentioned cause the tanning-liquor to become very sour, so that after its application the leather takes on free acids at the same time which are d-iflicult or quite'impossible to remove. The above-mentioned disadvantages are entirely overcome inthe process forming the object of the present invention: In my process the raw hide, or skin, is laid in a solution of salts of iron or other suitable ferro salts,

- the nitrogen monoxide (NO) is introduced,

whereby any additional oxygen must be avoided. The nitric monoxide must be practically free from higher nitric oxides. Only when the solution of the compound ferro salts has completely penetrated the skin, so that the section is of uniform colour, do I begin to oxidize.

An important point in the process is that, in the first phase of the tanning, the formation of higher nitric oxides, such as N 0 N0 HNO HNO which always occur in the processes hitherto adopted, is avoided, and that nitric monoxide is used entirely alone. The dark violet solution of the compound salts has the characteristic of being absorbed by the animal fibre without attacking it in the slightest degree.

The raw hides or skins are first placed in sulphate of iron liquor of a definite concentration and after some time nitric monoxide NO, which must not contain any higher nitric oxides, is introduced into the liquor, whereby the above-mentioned compound salts are formed, which are very thoroughly and u'niformly absorbed by the animal fibre. If the raw hides 0r skins so treated are then treated with oxygen-by simply blowing air against them or adding oxygen under; pressurethe fibre will be tanned in a, surprisingly uniform and thorough manner.

The leather obtained in this way shows, in contradistinction to the kinds of leather hitherto obtained by iron tanning, a completely undamaged fibre, so that the leather is ex tremely tough, flexible and strong.

Example A solution of sulphate of iron with 180400 g. FeSO 7H O to the litre is treated with nitric monoxide which is practically free from higher nitric oxides (no air being admitted) until no more NO is absorbed.

I The quantity varies according to the temperature and concentration of the solution or the pressure of the nitric monoxide. It is sufiicient it about 1 cubic metre of NO is absorbed in one cubic metre of fluid. In the solution thus prepared, the raw hides or skins from which the lime has been extracted are quickly introduced, and, according to the thickness, are allowed to stand in the solution for 2424 hours. They are then taken out and dried in the air and only washed after drying.

The raw hides or skins can also be placed first in the iron liquor, the nitric monoxide being in this case only introduced afterwards. For 100 kilos of hide 10-15 kilos of'salts of iron (reckoned as Fe O are required.

Instead of sulphate of iron, other divalent salts of iron which absorb nitric monoxide can be used, such as ferro chloride (FeCl or ferro acetate. The treatment with oxygen can also be extended for any desired period without damaging the fibre.

Having now described my invention, what I claim and desire to secure by Letters Patent 1s 1. Process for tanning animal hides using basic salts of iron, consistingin treating the hides with a solution of divalent salts of iron, then introducing into the solution substantially pure nitric monoxide and then oxidizing the hides.

2. Process in accordance with claim 1, wherein the hides are first placed in the solution of ferro salts and then pure nitric monoxide introduced.

3. Process in accordance with claim 1 subjecting the treated hides to the action of air or oxygen under pressure.

4:. A process for tanning animal hides consisting in treating the skins with a solution of divalent salts of iron, which has previously absorbed nitric monoxide.

5. A process as set forth in claim 4, consisting in first bringing the hides into the solution of form salts whereupon pure nitric monoxide is introduced.

In testimony whereof, I have signed my name to this specification at Berlin this 29th day of January, 1929.

KURT STI lRMER. 

